Diffusion transfer to stratum of a silver image inked and used in printing



NOV. 30, 1955 E H, LAND ETAL 3,220,837

DIFFUSION TRANSFER TO STRATUM 0F A SILVER IMAGE INKED AND USED IN PRINTING Filed July 22, 1955 IO- Phorosensirve Shee+ IO Suppori' 2O Silver Hcxlde S+rc+um {Soluhon of Salver Hclhde I6 x\\mm\\awu.wmmmm Developer und Solver 26 HIIHauHIIIIIuK Half-Pone PuHern Transferred *l'o Ink-Recepl'ive Surface ATTORNEYS United States Patent DIFFUSION TRANSFER T STRATUM 0F A SIL- VER IMAGE INKED AND USED IN PRINTING Edwin H. Land, Cambridge, and Mero M. Morse, Boston, Mass., assiguors to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Filed July 22, 1955, Ser. No. 523,792 7 Claims. (Cl. 96-29) The present invention relates to photomechanical reproduction and, more particularly, to the production of copies by mechanical printing from photographically prepared masters.

Conventionally, photomechanical reproduction involves the photographic formation of an invisible image in terms of the differentially hardened areas of a lightsensitive colloid such as bichromated gelatin. These areas may be differentially treated in a variety of ways to make the image useful for printing. For example, the unhardened areas may be inked to provide a hectograph for printing upon a sheet against which it is pressed, or may be dissolved to provide a stencil for transmitting ink to a sheet upon which it is superposed or to provide a relief useful in the etching of a metallic plate. Conventionally, if a photographic silver image is to be photomechanically reproduced, it first must be photographed in a differentially hardenable colloid of the foregoing type. In accordance with the present invention, a photographic silver image itself is differentially inked to effect photomechanical reproduction directly.

In accordance with thhe present invention, photomechanical production is effected by silver transfer-reversal prints that have been differentially inked. In a preferred silver transfer-reversal process, a silver halide developer and a silver halide solvent are applied in aqueous alkaline solution to a photoexposed silver halide stratum where they develop exposed silver halide to silver and react with unreduced silver halide to form a soluble silver complex. This complex is reduced to silver as a positive image on a silver-receptive stratum that is in superposition with the silver halide stratum. The silver halide stratum is stripped from the silver-receptive stratum when the positive image is completely formed. The shadows of this image are in terms of silvered areas of the silverreceptive stratum, the highlights in terms of unsilvered areas. It has been found that the silvered areas are hydrophobic in contrast to the unsilvered areas which are hydrophilic. Because of this differential ainity for water, the image is useful as a photomechanical master capable of being provided with a printing medium. For example, in conventional fashion, the image may be subjected first to a swab in order to moisten the unsilvered areas and then to a roller in order to coat the silvered areas with a greasy ink. A pictorial subject having continuous gradations of density may be copied in the foregoing way with the aid of a halftone screen.

Accordingly, the primary objects of the present invention are: to provide processes and products for printing by a photomechanical master, the printing surface of which has an image in terms of hydrophilic unsilvered areas and hydrophobic silvered areas for the dierential reception of a printing medium; to provide processes and products for printing by a photomechanical master of the foregoing type, the silvered areas of which are formed by silver transfer reversal; and to provide processes and products for printing by a photomechanical master of the foregoing type, the image of which is in halftone.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic perspective view of a lens and a halftone screen for photoexposing a photosensitive sheet to be used in accordance with the present invention; and

FIG. 2 shows successive, exaggerated, sectional views of the photosensitive sheet and an image-receptive sheet undergoing a process of the present invention.

FIG. 1 illustrates a Photosensitive silver halide sheet 10 being photoexposed in conventional fashion through an objective 12 and a halftone screen 14. This halftone screen 14, in one form, comprises two sheets of glass adjacent faces of which are ruled with fine parallel black lines, the lines of one face being perpendicular to the lines of the other to provide a fine grating. Ordinarily, the uniformly spaced lines range from 45 to 500 per inch. Although the photoexposure of sheet 10 here is made through a halftone screen, it is to be understood that where the subject contains only two densities with no intermediate gradations, as in the case of black-andwhite printed matter, no halftone screen is needed.

In FIG. 2, a processing composition 16 is shown as having been spread between Photosensitive sheet 10 and an image-receptive sheet 18, for example by advancing the sheets between a pair of pressure-applying nollers (not shown). Photosensitive sheet 10 comprises a support 20 and a silver halide stratum 22. Image-receptive sheet 1S comprises a support 24 and a silver-receptive stratum 26. Processing composition 16 is an aqueous alkaline solution of a silver halide developer, a silver halide solvent and a viscosity-increasing, film-forming material. Once spread, composition 16, Within a predetermined period, of the order of 40 to 120 seconds in duration, forms a negative image in silver halide stratum 22 by reducing silver halide to silver, and forms a positive image by reacting with unreduced silver halide to form a complex silver salt which migrates to stratum 26 where it is reduced to silver. Now, when sheet 10, together with layer of processing composition 16, is stripped from sheet 18, the positive image is available for differential reception of a printing ink.

In one procedure, at this point, it is desirable, though not necessary, to ensure that the unsilvered areas of the positive image are adequately moistened as by means of a swab charged with an aqueous solution. Thereafter, the silvered areas of the positive image may be provided with a printing ink 30 by means of a roller. The image now is either pressed into contact with an ink-receptive sheet or is mounted on the master cylinder of an offset machine for receiving ink and transmitting it to the rubberized fabric blanket of a reverse cylinder for deposit on the ink-receptive sheet.

Silver halide stratum 22, in one form, contains one or more of the silver halides, of which silver chloride, silver bromide and silver iodide are examples, dispersed in a suitable protective colloid, for example gelatin, collodion, cellulosics, vinylpolymers and linear polyamides. Examples of specific formulations of conventional emulsions suitable for such use are described in T. T. Baker, Photographic Emulsion Technique, American Photographic Publishing Company, Boston, 1948, Chapter IV. For best results, stratum 22 is a gelatino, silver halide, fine grain emulsion of high contrast and density. Commercially available, gelatino silver halide emulsions which have been found to produce good results are sold by Du Pont under the trade designations, X-Ray Fine Grain Industrial 506," Superior 3, Fine Grain Pan, Fine Grain Safety Positive, Photowrit and Photolith, by Kodak under the trade designation, Fine Grain Positive, and by Industrial Photo Products under the trade designation, Industrial Copy.

Silver-receptive stratum 26 provides one of the vigorous silver precipitating environments described in Patents Nos. 2,698,237 and 2,698,245, issued to Edwin H. Land on December 28, 1954. Such an environment includes silver precipitating nuclei such as the heavy metal suldes and/or selenides, the colloidal noble metals, or organic thio compounds dispersed in a macroscopically continuous vehicle kcomprising a water-permeable, inorganic, preferably siliceous, material. This material may contain, in colloidal or finely divided condition, oxides of silicon, particularly those in the form of silicic acids like silica aerogel, and mineral silicates such as mica and talc. Preferably, silver-receptive stratum 26 is from 1 to 8 microns thick.

Composition 16 comprises an aqueous alkaline solution of a silver halide developer and a silver halide solvent. Suitable developers are benzene derivatives having at least two hydroxyl and/or amino groups substituted in ortho or para position on the benzene nucleus. Examples of such developers are hydroquinone, amidol, metol, glycin, p-aminophenol and pyrogallol. Examples of silver halide solvents suitable for such use are conventional xing agents such as sodium thiosulfate, sodium thiocyanate and others described in Patent No. 2,543,181, issued to Edwin H. Land on February 27, 1951. Though not necessary, it `may be desirable to incorporate in the solution a film-forming material such as a water-soluble polymer, starch or gum for imparting a viscosity of 100 to 200,000 centipoises at a temperature of 20 C.

Supports 20 and 24, for example, may be composed of a paper, a glass, or a plastic.` Preferably, there is interposed between silver-receptive stratum 26 and sup` port 24 a water-impermeable stratum 28. This waterimpermeable stratum helps render areas of silver-receptive stratum 26 hydrophobic by preventing penetration of moisture from processing liquid 16 into support 24.v This water-impermeable stratum, for example, may be composed of unplasticized polymethacrylie acid or one of the cellulosic esters such as cellulose nitrate, cellulose acetate, cellulose butyrate, cellulose propionate, cellulose acetate butyrate, or cellulose acetate propionate. Preferred, however, are such rubbery polymers as polyvinyl butyral. If support 24 is water impermeable, of course, a discrete water-impermeable stratum need not be provided.

The positive print is formed in silver-receptive stratum 26 of tine silver particles concentrated primarily at its surface in thin but essentially continuous dense masses. In contrast, the silver deposited by development in silver halide stratum 22 is sparsely dispersed, silver halide stratum 22 being thick relative to silver-receptive stratum 26. Because of the condition of the silver in the positive image, sheet 18 may be used as a master in photomechanical reproduction either with or without further treatment for adapting it to be used with any particular ink. The significance of the condition ofthe silver is emphasized by the fact that the silvered areas are useful in printing, retaining their hydrophobic character even though their silver is oxidized to silver halide, for example, by reaction with an alkali halide, such as sodium or potassium bromide, in the presence of an alkali ferricyanide such as sodium or potassium ferricyanide. As used herein, the expression silvered areas is intended to include silvered areas containing oxidized rather than reduced silver.

The silvered areas, after the print has been moistened, may be provided, 'for example, with one of the inks sold by Interchemical Corporation Printing Ink Division, such as that designated by I.P.I. Satin Black. As will be apparent to persons skilled in the art, either the silvered or unsilvered areas of the image may be inked, depending on the specic treatment of the. print after formation. Examples of copy papers which are adapted to receive ink from images of the foregoing type are: that sold by Champion Paper & Fiber Company under the trade name, Krome Koat, commercially available alpha pulp; and commercially available baryta paper that is coated with silica aerogel.

Example A specific process of the foregoing type was carried out with the following materials: silver halide stratum 22 was a gelatino iodobromide emulsion of moderate speed, high contrast and high density sold by Kodak under the trade name, .Kodak Fine Grain Positive; silver-receptive stratum 26 contained as silver precipitating nuclei heavy metal suliides and selenides dispersed in a matrix of silica aerogel; and the formulation of processing composition 16 was as follows:

vWater cc-- 1860.0 Hydroquinone ng..- 52.0 Sodium thiosulfate g 43.5 Sodium hydroxide g 74.6 Sodium sullite g 78.0 Citric acid g 38.5 Sodium carboxymethyl cellulose g-- 93.0

The foregoing materials were processed as follows: Photosensitive sheet 10 kand image-receptive sheet 18, together with a rupturable container of processing composition 16, were advanced between a pair of pressureapplying rollers in order to spread the processing composition in a thin layer from one to ve thousandths of an inch thick between the adjacent surfaces of silver halide stratum 22 and silver-receptive stratum 26. The sheets werek maintained in superposed relation for a period of approximately 60 seconds. At the end of this period, sheet 10, together with a layer of processing composition 16, was stripped from sheet 18 to expose a positive print in silver-receptive stratum 26. This positive print was swabbed with a solution of the following formulation:

Water cc 67.0 Glycerine cc `30.0 Formaldehyde g 1.0 Monobasic ammonium phosphate g 2.0

The print then was rolled with .a greasy ink lsold by Multilith Corporation under the trade designation, Duro Clear Writing Fuid No. l0-2516A. This ink adhered only to the silvered portions of silver-receptive stratum 26. Finally, the print was pressed into contact with copy paper by means of a heavy steel roller. In this way, four good copies and three paler copies were produced without re-inking.

The present invention thus provides a simple photographic process for producing a master for photomechanical printing.

Since certain changes may be made in the process and product above referred to without departing from the scope of the invention herein involved, it is intended that all matter containing in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A process comprising the ysteps of applying, to a photoexposed gelatino silver halide stratum and a silverreceptive stratum, an aqueous alkaline solution of a silver halide developer and a silver halide solvent fixer, reducing exposed silver halide in the silver halide stratum to silver, forming from unreduced silver ,halide in the silver halide stratum a water-soluble complex silver salt,

difusing the salt to the silver-receptive stratum, producing from the salt on the silver-receptive stratum a visible image, -said image having first areas that contain silver concentrated primarily at the surface of said silverreceptive stratum in thin but essentially continuous dense masses and second areas that are substantially silver free, stripping the -silver halide stratum from the silverreceptive stratum, coating said first areas with a greasy ink after moistening said second areas with a liquid containing water, and pressing the image onto a copy sheet in order to transfer said greasy ink thereto.

2. The process of claim 1 wherein said first areas are in a half-tone pattern.

3. The process of claim 1 wherein the silver in said first areas is elemental.

4. The process of claim 1 wherein the silver in said first areas is reacted after formation with another material to form a silver compound.

5. The process of claim 1 wherein the silver of said first areas is reacted With an alkali halide in the presence of an alkali ferricyanide to form silver halide.

6. A process comprising the steps of applying, to a photoexposed gelatino silver halide stratum and a silverreceptive stratum, -an aqueous alkaline solution of a silver halide developer and a silver halide solvent fixer, reducing exposed silver halide in the silver halide stratum to silver, forming from unreduced silver halide in the silver halide stratum a Water-soluble complex silver salt, difI'using the `salt to the silver-receptive stratum, producing from the salt on the silver-receptive stratum a visible image, said image having iirst areas that contain silver concen trated primarily at the surface of said silver-receptive stratum in thin but essentially continuous dense masses and second areas that are substantially silver free, stripping the silver halide stratum from the silver-receptive stratum, coating said first areas with a greasy ink after moistening said second areas with a liquid containing water, and pressing the image onto la copy sheet in order to transfer said greasy ink thereto, said silver-receptive stratum being siliceous and being backed by a water-proof stratum.

7. A process comprising the steps of applying to a photoexposed silver halide stratum and a superposed hydrophilic, water-receptive, silver-receptive stratum which contains nuclei for precipitation of silver from a watersoluble silver complex, an aqueous alkaline solution of a silver halide developer and a silver halide solvent, reducing the exposed silver halide in the silver halide stratum to silver, forming from unreduced silver halide in the silver halide stratum a water-soluble silver complex, diffusing the complex to the silver-receptive stratum, producing from the complex in conjunction With said nuclei a visible image on the silver-receptive stratum, said image having first areas that contain silver concentrated primarily at the surface of said silver-receptive stratum in thin but substantially continuous, oleophilic dense masses and second areas that are substantially silver-free, thereafter stripping the silver halide stratum from the silver-receptive stratum, coating said silver-receptive stratum with an ink which will preferentially Wet said iirst areas, and pressing the image onto a copy sheet in order to transfer said ink thereto.

References Cited by the Examiner UNITED STATES PATENTS 1,811,734 6/1931 Trist 95-5.4 X 2,384,857 9/1945 Terry 95-5.4 2,702,244 2/ 1955 Land. 2,725,298 11/1955 Yutzy et al. 96-28 2,763,553 9/1956 Clark et al 96-33 X OTHER REFERENCES Photolithography, B. E. Tory, Graphic Arts Monthly, published in Australia in July 1953 (pp. 182-184).

NORMAN G. TORCHIN, Primary Examiner.

PHILIP E. MANGAN, Examiner. 

7. A PROCESS COMPRISING THE STEPS OF APPLYING TO A PHOTOEXPOSED SILVER HALIDE STRATUM AND A SUPERPOSED HYDROPHILIC, WATER-RECEPTIVE, SILVER-RECEPTIVE STRATUM WHICH CONTAINS NUCLEI FOR PRECIPITATION OF SILVER FROM A WATERSOLUBLE SILVER COMPLEX, AND AQUEOUS ALKALINE SOLUTION OF A SILVER HALIDE DEVELOPER AND A SILVER HALIDE SOLVENT, REDUCING THE EXPOSED SILVER HALIDE IN THE SILVER HALIDE STRATUM TO SILVER, FORMING FROM UNREDUCED SILVER HALIDE IN THE SILVER HALIDE STRATUM A WATER-SOLUBLE SILVER COMPLEX, DIFFUSING THE COMPLEX TO THE SILVER-RECEPTIVE STRATUM, PRODUCING FROM THE COMPLEX IN CONJUNCTION WITH SAID NUCLEI A VISIBLE IMAGE OF THE SILVER-RECEPTIVE STRATUM, SAID IMAGE HAVING FIRST AREAS THAT CONTAIN SILVER CONCENTRATED PRIMARILY AT THE SURFACE OF SAID SILVER-RECEPTIVE STRATUM IN THIN BUT SUBSTANTIALLY CONTINUOUS, OLEOPHILIC DENSE MASSES AND SECOND AREAS THAT ARE SUBSTANTIALLY SILVER-FREE, THEREAFTER STRIPPING THE SILVER HALIDE STRATUM FROM THE SILVER-RECEPTIVE STRATUM, COATING SAID SILVER-RECEPTIVE STRATUM WITH AN INK WHICH WILL PREFERENTIALLY WET SAID FIRST AREAS, AND PRESSING THE IMAGE ONTO A COPY SHEET IN ORDER TO TRANSFER SAID INK THERETO. 